1. Field of the Invention
This invention relates to hybrid electric vehicles, and more particularly to a method and system for managing the various inputs that determine the on/off state of the engine in a hybrid electric vehicle.
2. Background Art
A typical powertrain for a hybrid electric vehicle has at least two sources of power. One source typically is an internal combustion engine, and the second source is a high voltage electric motor, usually an induction motor. There are three general classes of hybrid electric vehicle powertrains; i.e., parallel, series and parallel-series.
A parallel hybrid electric vehicle powertrain usually includes an internal combustion engine, one or more electric motors, and an energy storage device, usually a battery. Mechanical power from both the engine and the electric motor(s) is directly available to propel the vehicle.
A series hybrid electric powertrain includes an engine, a generator, an electric motor, and an energy storage device, usually a battery. The electric motor is the only source of mechanical power that is directly available to propel the vehicle. Power from the engine is electrically routed from the generator to the electric motor.
A parallel-series hybrid electric powertrain configuration is a combination of parallel and series configurations. It is capable of operating in a first operating mode with characteristics of a parallel hybrid electric powertrain and in a second operating mode with characteristics of a series hybrid electric powertrain.
Each of the three powertrain configurations described previously is capable of propelling the vehicle by power from the electric motor power alone, with or without the engine running to produce power. Typically there are many factors that determine whether it is desirable to run the engine or not, including those affecting safety, fuel economy, performance, and passenger comfort. An electronic vehicle controller with powertrain control software is responsible for considering these factors and making the complex decision to run the engine or not.
Because of the large number of inputs that must be evaluated by the powertrain control module as factors in determining the desired engine state, the control module software architecture must provide a means of organization and prioritization of these inputs. In addition, due to the fact that the inputs may change throughout the design phases of vehicle development, the software architecture must be flexible enough to maintain this organization in spite of modifications.